#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Software: PyCharm
# @Version : Python-
# @Author  : Shengji He
# @Email   : hsjbit@163.com
# @File    : LemonadeChange.py
# @Time    : 2020/12/10 14:55
# @Description:
from typing import List


class Solution:
    def lemonadeChange(self, bills: List[int]) -> bool:
        """
        At a lemonade stand, each lemonade costs $5. 

        Customers are standing in a queue to buy from you, and order one at a time (in the order specified by bills).

        Each customer will only buy one lemonade and pay with either a $5, $10, or $20 bill.  You must provide the
        correct change to each customer, so that the net transaction is that the customer pays $5.

        Note that you don't have any change in hand at first.

        Return true if and only if you can provide every customer with correct change.

        Example 1:
            Input: [5,5,5,10,20]
            Output: true
            Explanation:
            From the first 3 customers, we collect three $5 bills in order.
            From the fourth customer, we collect a $10 bill and give back a $5.
            From the fifth customer, we give a $10 bill and a $5 bill.
            Since all customers got correct change, we output true.
        Example 2:
            Input: [5,5,10]
            Output: true
        Example 3:
            Input: [10,10]
            Output: false
        Example 4:
            Input: [5,5,10,10,20]
            Output: false
            Explanation:
            From the first two customers in order, we collect two $5 bills.
            For the next two customers in order, we collect a $10 bill and give back a $5 bill.
            For the last customer, we can't give change of $15 back because we only have two $10 bills.
            Since not every customer received correct change, the answer is false.

        Note:
            - 0 <= bills.length <= 10000
            - bills[i] will be either 5, 10, or 20.

        :param bills: 
        :return: 
        """
        five, ten = 0, 0
        for bill in bills:
            if bill == 5:
                five += 1
            elif bill == 10:
                if five == 0:
                    return False
                five -= 1
                ten += 1
            else:
                if five > 0 and ten > 0:
                    five -= 1
                    ten -= 1
                elif five >= 3:
                    five -= 3
                else:
                    return False
        return True


if __name__ == '__main__':
    S = Solution()
    bills = [5, 5, 5, 10, 20]
    print(S.lemonadeChange(bills))
    print('done')
